Apparatus for pressure die-casting



Oct. 31, 1933. J. E. HOY

} APPARATUS FOR PRESSURE DIE CASTING Filed Aug. 29, 1932 INVENTOR Jbkn .2 3. Ray BY M'Z9W% 52 ATTORNEY Patented Oct. 31, 1 933 APPARATUS FOR PRESSURE DIE-CASTING John E. Hoy, Midland. Mich., 'assignor to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application August 29, 1932. Serial No. 630,757

3 Claims.

The invention relates to pressure-die-casting apparatus; and particularly to an improvement in such apparatus whereby the inclusion of oxidation products in finished die-castings is prevented.

In diecasting metals which oxidize in air, or form surface coatings on the molten metal which if admitted to the mold would injure the casting, means and methods are desirable to prevent such surface coatings from entering the mold. This is particularly true when die-casting magnesium owing to the extreme readiness with which magnesium oxidizes and acquires a surface coating when at the elevated temperatures encountered in such practice. Die-casting machines essentially comprising a melting pot having movably mounted therein a casting vessel having a discharge port positioned to be submerged in the molten metal in the crucible but adapted to be elevated out of the metal by movement of the casting vessel have been utilized.' However, in using such apparatus it has been found that oxidation prod ucts on the surface of the molten metal are caught in the discharge port of the castingvessel as it is moved out of the metal and are forced into the mold, resulting in flaws in the finished casting. Also, the movement of the casting vessel in and out of the molten metal tends to cause the oxidation products on the surface thereof to be entrained in the molten metal in the crucible and thus contaminate the whole body of metal.

To eliminate the foregoing difllculty apparatus has been devised wherein the casting vessel is fixed within the crucible and has a nozzle fixed on the end thereof for discharging the molten metal therefrom and is provided with a valve member whereby filling of the casting vessel below the surface of the metal can be accomplished. This apparatus prevents oxidation crust inclusions in the finished castings but has the disadvantage cf requiring intricate construction for heating the nozzle and even so is subject to frequent freezing of the metal therein, thus causing costly delay for clearing the nozzle of solid metal.

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ever, but one of the various ways in which the principle of the invention may be used.

In said annexed drawing:

Figure 1 shows a part vertical cross-section of our apparatus.

Figure 2 is a vertical section in part, showing the discharge end of the casting vessel and nozzle arrangement with various surrounding elements when such vessel is in position to permit filling thereof with molten metal from the crucible. l

I have found that the diificulties inherent in the design and operation of prior apparatus for pressure-die-casting metals, particularly magnesium, can be eliminated by a novel arrangement of certain structural elements of die-casting apparatus in combination with a special type of nozzle as a new element. This special nozzle is slidably mounted in the melting crucible cover and, at one end, projects below the surface of the molten metal in the crucible and is at that end adapted to engage with the tip of the casting vessel. The other end of the nozzle projects through the cover of the melting crucible and is adapted to engage with the die-mold inlet for molten metal, or with a nipple plate 25 which guides the nozzle tip to the die-mold inlet.

The covered crucible has a pressure casting vessel fixedly mounted therein, and is pivoted in such manner that the crucible with its contents may be elevated and depressed substantially vertically as desired. The nozzle member provides a connection behvcen the casting "vessel and a die-mold wherethrough molten metal may be transferred to the mold, and serves as a valve member whereby metal may be admitted to the casting vessel. Further, the arrangement of the structural elements is such that the connection between the nozzle and the casting vessel is always broken below the surface of the molten metal in the crucible, and also, so that the molten metal in the nozzle can run back into the crucible I until the level of the metal therein coincides with the level of the metal in the crucible, thereby maintaining the nozzle substantially free of metal during nonuse thereof thus preventing freezing of metal therein.

So that the invention may be more clearly understood, reference is made to the drawing which illustrates a preferred embodiment of my improved die-casting apparatus. Figure 1 shows the apparatus in position for discharging molten magnesium into a die-mold. The melting crucible 1, attached at its rim as by cap screws to a cover 2 therefor, is movably disposed within a fire box 8 equipped with a heating burner 4. The crucible cover 2, from which the crucible 1 is suspended, is here shown integral with the bifurcated arm 5 of lever 6 and with a casting vessel 7 disposed within the crucible 1, and is associated with the nozzle member 17. The lever 6 is pivoted on a pin 8 and has another arm comprising a shaft extension 9 with a counterweight 10 depending therefrom whereby substantially vertical movement of the crucible and its contents is facilitated. The crucible cover 2 has an opening 11 therein, normally closed by a hinged cover 12, through which magnesium may be introduced into the melting crucible 1. The casting vessel l comprises a chamber 1% having a pipe 13 for admitting a suitable fluid under pressure thereinto, and a duct 15 connecting at the lower end of the chamber 14 and having at its other extremity an outlet and inlet tip 16 adapted to engage below the surface of the molten metal in the crucible 1 with a vertically slidable nozzle 17. The nozzle member 17 is adapted to engage at its lower end with the tip 16 of the casting vessel '7 and at its up er and with a suitable die-mold 18. A nipple plate 25 may be provided to guide the nozzle tip to the die-mold inlet. A bracket 19 supported as by the fire box 3 provides a stop 20 for engaging a flange on the nozzle 17 when the crucible is depressed, thereby arresting its vertical descent.

Figure 2 shows the position of the nozzle 17,. with various associated elements, after the crucible is depressed by lowering the arms 5, and the connections between the nozzle 1'7 and the die-mold 18 and between the nozzle 1? and the casting vessel tip 16 are broken.

The operation of the apparatus as exemplified in the preferred embodiment of my invention will now be described with reference to the drawing. Figure 1 shows the apparatus in position for filling the die-mold 18. By operating a suitable valve 23 a fluid under pressure, such as air, nitrogen, etc., is admitted through the pipe 13 into the chamber 14 thus causing the molten metal 21 in the casting vessel 7 to flow through the nozzle 17 into the die-mold 18 until the mold is substantially filled therewith. When the casting operation is completed the fluid pressure in the chamber 14 is vented in any convenient manner as by valve 24, and the counterweight 10 is elevated whereby the crucible is depressed. This action results, first, in breaking the connection between the upper end of the nozzle 17 and the die-mold 18 thereby permitting removal of the mold containing the casting. Second, the nozzle descends and comes to rest upon the stop 20. provided therefor, and

third, the connection between the casting vessel tip 16 and the nozzle 17 is broken beneath the surface of the metal in the crucible. The severance of the connection between thenozzle and casting vessel permits the molten metal 22 in the crucible 1 to flow by gravity through the tip 16 into the duct 15 and chamber 14 of the casting vessel 7, and, the metal contained in the nozzle 17. to flow therefrom into the crucible 1 thereby preventing freezing of the metal in the nozzle between successive existing operations. An empty die-mold may then be substituted for the filled mold, the crucible re-elevated thereby n aging thetip, 16 of the casting vessel '1 with the nozzle 17 below the surface of the metal in the crucible and then enga in the nozzle with the fresh die-mold, thus restoring the apparatus members to their original position. Raw

magnesium is introduced into the melting crucible from time to time in order to maintain the level of the molten metal therein substantially above the level of the filling orifice in the tip 16.

From the foregoing it will be comprehended that the vertically slidable nozzle member of my improved die-casting apparatus performs a number of functions. Thus, the nozzle serves as a means wherethrough molten metal may be transferred from the casting vessel to a die-mold; as a valve member whereby molten metal is admitted to the casting vessel from below the surface of the molten metal in the melting crucible; and is self-emptying during nonuse thereby avoiding the necessity 'of heating thereof to prevent metal freezing therein during such nonuse My improved apparatus may be employed in casting any desired metal but employment thereof in casing magnesium is especially advantageous. It will be readily apparent to those skilled in the art that various modifications of the specific structure and details hereinbefore shown can be made without departing from the scope of my invention. For instance, it is obvious that the casting vessel may be movable relative to the crucible; that in such case the crucible may be either fixed or movable; that the bracket stop for interrupting the downward descent of the slidable nozzle may be carried by, or constitute a part of, the crucible if same is fixed and the casting vessel movable therein; and that many similar minor changes can be made in the apps.- ratus described.

The term magnesium is used herein and in the appended claims to means not only elemental magnesium but also alloys thereof wherein the magnesium content predominates.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the apparatus herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In die-casting apparatus, the combination of a melting crucible; a pressure casting vessel fixedly mounted within said crucible and having an upwardly directed combination inlet and outlet port through which molten metal may be discharged from, and admitted into, said vessel; controllable means to introduce a pressure fluid into the said casting vessel; a vertically slidable nozzle adapted to engage at its lower end with the said outlet port below the surface of the molten metal in the crucible and to engage at its upper end with the inlet of a die-mold; means to elevate said crucible and casting vessel, whereby said nozzle can be engaged with the said inlet and outlet port and said die-mold to form a continuous passage wherethrough molten metal can be delivered from the casting vessel into the mold, and to depress said crucible, whereby said nozzle can be disengaged from said mold; and a stop to arrest the vertical descent of said nozzle during depression of said crucible, whereby said nozzle can be disengaged from said inlet and outlet port and the fluid content of said nozzle can drain by gravity into said crucible.

2. In apparatus for die-casting magnesium, the combination of a melting crucible; a pressure casting vessel fixedly mounted within said crucible including an upwardly directed combination inlet and outlet port through which molten maginto, said vessel; controllable means to introduce a pressure fluid into the said casting vessel; a vertically slidable nozzle adapted to engage at its lower end with the said outlet port below the surface of the molten magnesium in the crucible and to engage at its upper end with the inlet of a die-mold; means to elevate said crucible, whereby said nozzle can be engaged with the said outlet port and said die-mold to form a continuous passage wherethrough molten magnesium can be delivered from the casting vessel into the mold, and to depress said crucible, whereby said nozzle can be disengaged from said mold; and a stop to arrest the vertical descent of said nozzle during depression of said crucible, whereby said nozzle can be disengaged from said outlet means below the surface of the molten magnesium in said crucible, and the molten magnesium in said nozzle can drain by gravity into said crucible.

3. In die-casting apparatus having a melting crucible and a pressure casting vuael therein; a vertically slidable nozzle adapted to engage at its lower end with the discharge outlet of the pressure casting vessel below the suriace of the molten metal in the crucible and to engage at its upper end with the inlet or a die-mold to form a continuous passage wherethrough molten metal can be delivered from the casting vessel to the die-mold and adapted to drain its fluid content when disengaged from the said die-mold and through.

JOHN E. HOY. 

